Automatic telephone system



Nov. 12, 1935. J. H. Voss' ET A1.

` AUTOMATIC TELEPHONE SYSTEM J. H. VOSS ET AL AUTOMATIC TELEPHONE SYSTEM Novw 12, 1935.

Filed Sept. 5, 1933 2 Sheets-Sheet 2 'Patented Nov, 12, 1935 UNITED STATES AU'roMA'rIc TELEPHONE SYSTEM John H. Voss.' Downers Grove, and Harry N. Newstedt, Chicago, lll., assgnors to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application September 5, 1933, Serial No. 688,102

22 Claims.

'I'his invention relates to automatic telephone systems in general, but relates more particularly to small systems of the character commonly known as private automatic exchanges. These systems as a rule are privately owned by individuals or corporations and are installed in factories and other establishments for providing local service between a small number of local telephone lines and for providing connections over trunk lines tothe main olice of a .telephone companys network.

The object of the invention is to provide means whereby a minimum number of switching devices will be employed for completing the desired telephone connections, and which will enable the equipment to be manufactured very cheaply while retaining all the features necessary for modern high-class and dependable telephone service.

One of the featuresof the invention relates to the means for enabling local subscribers to transfer trunk connections to desired local subscribers lines and at the same time maintain the trunk in use busy to the remaining other local subscribers lines.

Another feature relates to the simplified circuit arrangements for enabling any local subscriber to connect with an idle trunk after which such trunk is made busy to the remaininglocal subscribers lines.

A further feature of the invention relates to the provision of a two-relay allotter which alternat-ely selects the two nder connector links for use and which also seizes the idle one of the links in case the other link normally selected By tli'allotter is busy when a call is initiated.

Other features, together with the ones named above, will 4be explained hereinafter, reference being, had to the accompanying drawings comprising Figs. l and 2 which show by means of the usual circuit diagrams a sufficient amount of apparatus to enable the invention to be understood.

Fig. 1 illustrates a local subscribers line and its individual equipment, the common start equipment and two trunks connected to a distant central office.

Fig. 2 illustrates a finder connector link comprising the finder F, the connector C, and the interposed relay group, and a local subscribers line indicated by the dotted rectangle in the upper right hand corner.

Referring now to Fig. l in detail, all subscribers, such as subscriber #5, are equipped with a standard and well-known monophone set. Each set comprises a handset T and R, a calling device CD, a cradle and cradle spring CS, an induction coil IC, and the ringer bells RB. Each line has a local line circuit, the'conductors of which terminate in the local finder and con-V nector banks for completing local calls. Attached 5 to the base of each standard monophone set is a sub-base having a number of spring assemblies and keys which are operated when originating or receiving trunk calls. Each sub-base has two keys 'IK-I and TK-Z for originating 10 and answering trunk calls. A push button PB is also provided in the sub-base for flashing an operator in a trunk call to a manual exchange or for cancelling the digits dialled if an error has been made in dialling an .automatic subl5 scriber in either the local or a distant automatic exchange. Conductors extending from the spring assemblies controlled by these keys extend to the subscribers individual trunk relays 60 and 10 and from thence to the two central oiiice trunks I and 2. The conductors 8l to 86, inclusive, are multipled to all the subscribers individual trunk relays 60 and 10 as indicated in Fig. 1 and by those conductors shown extending to the dotted rectangle in Fig. 2. Each trunk is provided with a pair of relays, different toned ringers, such as TRI and TR2, or alternating current relays such as 88 and illV which control circuits for illuminating the different colored trunk lamps. The different colored lamps or different toned 80 ringers are located throughout the local estab- `lishment where the same are visible or audible to all the local subscribers. All local subscribers lines have an individual cut-ofi relay, such as relays 4 and |84, and all lines terminate in both 35 the finder and connector banks shown in Fig. 2. Relay 8 is a line relay common to all the subscribers lines and controls the start circuit for the lnder connector banks through the tworelay allotter comprising relays I 0 and Il.

The mechanical construction of the spring assemblies and keys in the sub-bases is shown and claimed in a copending application of H. F, Obergfell, Ser. No, 536,424, led May l1, 1931. Briefly the operation is as follows: When the handset is removed from the cradle, springs 53 and 54 automatically close. If either key TK-l or TK-Z is depressed, the bar 41 slides in a horizontal direction and by means o! bushings 48, 49 and 50 operates springs 5I, 52, 56, and 58. 50 Springs i are operated only when trunk key TK-Z is depressed. A mechanical lock (not shown) is provided for preventing either key from being operated when the other is operated. The catch bar 51 is operated responsive to the 55 removal of the handset from the cradle to position itself so that when'springs 52 and 55 are operated the same will be mechanically locked until the handset is replaced on the cradle irrespective of the subsequent operations c-f the keys. The keys TK-I and 'IK-2 are keys or levers which are moved olf center and remain in such positions until moved by hand back to normal or until the handset is replaced on the cradle, which automatically returns the keys to their normal positions. The push-button PB is of the selfrestoring type and Operates springs 46 only as long as the push-button is depressed.

'Ihe mechanism of the finders, such as F, and the connectors, such as C, is of the well-known rotary type, commonly used for rotary lineswitches, and the wipers of which move in a forward direction only and remain in the position last used. The circuit details of the connector are somewhat different from the finders in that the wipers of the connector are directively operated to a called line and are automatically restored to normal position after termination of the conversation.

In the case illustrated applicant has elected to show a system having a maximum of ten local lines having telephone numbers 1 'to 0, inclusive, and two finder connector links, such as shown in Fig. 2.

The subscribers cut-oil? relays, such as 4 and |84, and relayA |40, are two-step relays which close their contacts marked I in their first step and their contacts marked II in their second step. Relay |20 is a slow-to-operate relay which is also appreciably slow to release. Relays |30 and |80 are equipped with copper sleeves around their cores which render the relays slow to release.

Local connection armature 5, conductor 3|, resting contact of spring A56 and said spring, push-button springs 40, conductor I, through the calling substation loop, conductor 2, spring 5| and its resting contact, conductor 32, armature "I, and through the upper Winding of cut-off relay 4 to battery. Cutoff relay 4 is so adjusted that when the circuit is closed through theupper Winding armature 6 is the only armature operated. Relay 4 in operating its armature 6 marks the line as calling by connecting battery through its lower winding to the finder bankl and prepares a circuit for fully energizing itself over its lower winding when the finder finds the calling line. Common line relay 8 is operated over the above traced circuit and closes a circuit for a start relay of v an idle finder-connector link as follows: ground over this circuit, but relay and start relay |20 energize. Since the start relays of the finderconnector links are slow to operate relays, relay operates first and opens the start circuit to the second finder connector link at armature I4 before the start relay |20 of the second link has had time to fully operate. n

In case this finder-connector linkis busy, then armature |45 would be opened and the wiper |08 would not be in normal position; therefore no circuit is completed for relays and |20 and the start circuit would extend to the second finder-connector link by way of armature I4 and conductor I6 to start relay |20' and over a circuit similar to that traced, to battery. In case all of the finder-connector links are busy when a subscriber initiates a call such subscriber will not hear the dial tone and will either wait until dial tone is heard or will replace the handset on the cradle.

Returning now to when start relay |20 was energized in response to subscriber #5 initiating a call, said relay at armature 2| prepares the test circuit for relays |40 and |50, at armature |22 prepares a point in the circuit for energizing relay l0 over conductor I1, at armature |24 prepares a circuit for relay |50, and at armature |23 closes a circuit extending from ground at armature |5| and its resting contact for energizing the finder motor magnet |25. Magnet |25 energizes to position its pawl preparatory to stepping the wipers of the finder and near the end of its stroke closes armature |26 to complete a .circuit for energizing relay |50 by way of armature |24 and its lower winding. Relay |50 energizes and at armature |5| opens the circuit extending to magnet |25 which deenergizes and operates the wipers of the finder one step. The deenergization of magnet |25 also opens the circuit of relay |50 at armature |26, and the latter relay deenergizes to again close the circuit to the motor magnet. This interaction between relay |50 and magnet |25 continues until test wiper |02 encounters a calling battery potential. When Wiper |02 reaches the contact marked with calling battery potential a circuit may be traced for holding relay |50 energized and for energizing relay 40 as follows: from ground by way of the upper winding of relay |50, normally closed springs controlled by armature |4|, lower windr" ing of two-step relay |40, armature I2 I, test wiper |02 and engaged bank contact, conductor 33, armature 6 and through the lower Winding of cutoff relay 4, to battery. The relay |50 is held energized over this circuit in order to prevent the magnet |25 from energizing to step the wipers another step. Cut-off relay 4 energizes in its second step over the above-traced circuit. Twostep relay |40 energizes in its first step over the above-traced circuit to close only amature |43, which completes a circuit for energizing slow-torelease relay |30 by way of the working contact of armature |5|. Slow-to-release relay |30 at armature |32 connects ground to conductor I'I by way of armature |22 for energizing relay I0 and also connects ground through the upper winding of relay |40 for energizing the latter relay through its second step to operate armatures I4 I, |42, |44, and |45, at armature |34 prepares a point in the talking circuit as well as preparing a point in the impulsing circuit for relay |50, at armature |44 prepares a circuit for series relay and a circuit for the connector motor magnet |35, and at armature I3| and its resting contact opens a point in the wiper restoring circuit for the connector and at its working contact prepares a point in the testing circuit for the con- 'nector. At the normally closed springs controlled -relay |49 grounds wiper |02 and conductor 33 to fully energize cut-off relay 4 in its second step and to make this line busy to both finder and connector switches and at armature |44 prepares a point in the circuit for the slow-to-release series relay |80. At armature |45 relay |40 opens the circuit of start relay |20, which deenergizes after a short interval to open the start circuit. Relay |20, upon deenergizing, at armature |23 opens the circuit to the finder magnet |25, at armature I2| opens the circuit to the lower winding of relay |40, at armature |22 removes ground from conductor I1 but relay |0 is maintained energized over its local locking circuit, and at armature |24 opens the stepping circuit to the` lower winding of relay |50. Cut-off relay 4, upon energizing in its second step, disconnects the line conductors 3| and 32 from the upper winding of relay 4 and from common line relay 8, which deenergizes in case no other subscriber is initiating a call. When conductor |1 is grounded at armature 32 responsive to the energization of relay |39 relay l0 energizes through the normally closed springs controlled by armature I3 to battery through resistance |8. At armature I3 relay closes a local locking circuit for itself and at armature |2 prepares the start circuit for the second finder connector link.

All of the operations just described have taken place responsive to the #5 subscriber removing his handset from the cradle, and at this time dial tone is transmitted from conductor |29, normal contact and wiper |06, resting contact'of armature |6| and said armature, the tone condenser, and thence over the calling subscribers loop in the well-known manner.l n

Subscriber #5 may now dial the number of the desired subscribers line, in this case number 4. Responsive to the operation of the calling device CD at substation #5 for the digit 4, the circuit extending to relay I 50 is opened four times to deenergize relay |50 a corresponding number of times. At each deenergization of relay 50 the circuit of slow-to-release relay |30 is mo mentarily openedat armature I5| and its Work-y ing contact, but said relay, due to the copper sleeve around its relay core, maintains its armatures .attracted during the impulsing period. Each time relay |50 deenergizes, a circuit may be traced from grounded armature |5| and its resting contact, armature |33, armature |63, armature |91, and through the Winding of magnet to battery for energizing magnet |35 to operate its pawl preparatory to stepping the wipers of the connector. A branch of Athe above-traced circuit extends by way of armature |44 to the series relay |80 for energizing the latter relay. Relay |80 at armature |8| and its resting contact opens a point in the circuit of switching relay |90 and at its working rcontact prepares a point in the circuit for the lower winding of the combined busy and back bridge relay |50, and at armature |82 prepares a new impulsing circuit for magnet |35 independent of armature |63 which may be operated by the combined busy and back bridge relay |60 operating in response to the test wiper |01 passing over busy grounded contacts. After the rst impulse line relay reenergizes and opens the circuit of magnet |35 which releases and steps the Wipers one step. 5 The remaining impulses of the digit operate lthe line relay |50 and magnet |35 in the manner set forth toposltion the Wipers |06 to inclusive, on the fourth set of bank contacts, or the contacts terminating the line of substation #4. l0

Assuming that substation #4 is busy, then wiper |01 will encounter a ground connection on the fourth bank contact placed thereon by a nder or connector of another iinder connector link. In this case the combined back ridge and l5 busy relay is energized over a circuit extending from the busy grounded contact, wiper |01, armature |8| and its working contact, armature |95, resistance |14, and through the lower winding of relay |60 to battery. Relay |60, upon 20 energizing at armature |62 and its working contact prepares a locking circuit for itself, and at its resting contact opens the circuit to switching relay |90, at armature |63 opens a point in the initial impulsing circuit to magnet |35, and at 25 armature |6| completes a circuit for transmitting busy tone over the talking conductors to subscriber #5 from busy tone conductor |28, armature |92 and the tone condensers to the upper heavy talking conductor.

A short time after the transmission of the last digit, series relay deenergizes, and at the normally closed contacts controlled by armature |8| completes the locking circuit of relay |50 as follows: from grounded armature |93, armature 35 -|3| and its working contact, armature '|62 and its working contact, normally closed springs controlled by armature |8|, and through the resistance |14 and the lower winding of relay |60 to battery. When subscriber #5 hears the busy 40 tone such subscriber will replace the handset on the cradle and release thel connection in the same manner as will be described hereinafter.

Assuming now that substation #4 is idle instead of busy, then wiper |01 will not encounter a 45 grounded bank contact, and, therefore, relay |60 will not be energized. Therefore, when relay |80 deenergizes Lafter the impulsing period, a circuit may be traced for energizing switching relay and cut-off relay |84 as follows: from grounded 50 armature |93, armature |3| and its working contact, armature |62 and its resting contact, lower Winding of switching relay |90, resting contact of armature I8| and said armature, wiper |01, and through the upper Winding of cut-off relay |84, 55 to battery.

Cut-off relay |04 is operated over this circuit to operate its armatures |85 and |81 to disconnect the line conductors |66 and |68 from start conductor 3 and the lower winding of relay |84, and 50 to operate armature |86 to apply ground to conductor |61 via the bank contact and wiper |01 and operated armature |94 to busy this line in the finder banks. At armature |96 relay |90 closes a circuit from grounded armature |32 through its 65 upper winding for fully operating its remaining armatures. Relay |90, upon fully operating at armature |93 opens a point in the restoring circuit of the connector, at armature |92 opens a point in the busy tone circuit, at armature |94 connects direct ground to wiper |01 to busy the called line, at armature |95 opens a point in the circuit through the lower winding of relayl |60, at armatures |98 and |99 prepares circuits for transferring trunk calls, at armature |91 opens a 75 point in the impulsing circuit to magnet |35, and at armatures |9| and |89 connects interrupted generator Int. Gen. to the called line as follows: from interrupted generator conductor |21, armature |1| and its resting contact, armature |9|, wiper |06 and engaged bank contact, conductor |68, condenser and ringer at substation #4, conductor |66, wiper armature |89, armature |13 and its resting Contact, and through 'the lower winding of ring-cut-oif relay |10 to battery.

Standard ring-back tone is heard by the calling subscriber from conductor |21, resting contact of armature |1| and said armature, armature ISI, resting contact of armature |6| and said armature, and through the tone condensers to the heavy talking conductor and thence over the calling loop. When subscriber #4 answers by removing his handset from the cradle, the ring-cutoi relay |19 is energized over the substation loop and the ringing circuit just traced. At armatures |1| and |13, relay |10 disconnects the ringing circuit and completes the talking circuit by way of the working contacts of armatures |1| and |13 as well as completing the circuit for energizing relay 160, and at armature |12 completes a locking circuit for itself to grounded armature l32. The circuit for energizing the combined back bridge and busy relay |60 extends from ground through the upper winding of relay |60, working contact and armature 1|, armature |9|, wiper |06, conductor |68 over the called subscribers loop to conductor |66, wiper armature |89, armature |13 and working contact, and through the lower winding of relay |60 to battery. At armatures |64 and |65 relay |60 closes points in the circuits for transferring trunk calls. The calling subscriber #5 and called subscriber #4 are connected over the heavy talking conductors, the calling subscriber receiving talking battery from the windings of line relay |50 and the called subscriber receiving talking battery from the winding of relay |60.

After conversation and responsive to subscribers #5 and #4 replacing their receivers, line relay |50 and relay 60 deenergize and at armature |5| relay |50 opens the circuit of release relay |30, which deenergizes after a short interval. At armature |32 release relay |30 opens the locking circuits of relays |40, |10 and |90, and at armature |3| opens the locking circuit of relay |60 in case the latter relay is locked up on a busy call, whereupon said rela-ys deenergize. A circuit may now be traced for restoring the wipers of the connector to normal as follows: from grounded armature |93, armature |3| and its resting contact, multipled contacts engaged by wiper |08 and said wiper, interrupter springs |36 of magnet |35 and through the winding of magnet |35 to battery. Magnet |35 operates like a buzzer over the abovetraced circuit until wiper |08 no longer engages a grounded contact, at which time the wipers of the connector stop and remain in normal position or the position shown in the drawings.

The deenergization of relay |40 removes ground from wiper |92 and conductor 33 to deenergize the cut-off relay 4 at armature |42 and at armature |45 reestablishes the start circuit for relay |20. The deenergization of relay |10 at armatures |1| and 13 disconnectsthe relay |60 from the called line to deenergize the same in case the called party has not replaced his handset on the cradle. The deenergization of relay |60 opens points in the transfer circuits at armatures |64 and |65. The deenergization of relay opens the circuits to the called line at armatures |9| and |89, at armatures |93 and |91 closes the previously traced connector restoring circuit, at armatures |98 and |99 opens further points in the transfer circuits, and at armature |94 disconnects ground from wiper |01 to deenergize cut-off relay 5 |84. All of the relays with the exception of relay |0 are now dcenergized and in normal position. The wipers of the iinders remain in the positions last used, and, therefore, when the connector wipers reach their normal positions the nder- 10 connector link is available for another call.

Incoming trunk calls It will nc-w be assumed that an incoming trunk call is received over conductors 90 and 9| from 15 the distant ofce. When an incoming trunk call is received the application of ringing current to trunk conductors operates either the ringers TR2 or the alternating current relay 81 dependent upon which is provided. Relay 81 at its 20 armature closes the circuit from the commercial power source for lighting the trunk #2 red trunk lamps located throughout the establishment. Any subscriber upon observing the lighting of the trunk lamp may answer the call by operating 25 trunk key TK-2 and removing the handset from the cradle. Assuming that subscriber #5 answers this trunk call, the operation of key TK-Z springs 5|, 52, 55 and 56 are operated and in response to the removal of the handset from the cradle springs 30 53 and 54 are closed as previously described. A circuit may now be traced for energizing relay 10 as follows: from grounded springs 55, normally closed springs controlled by armature 64, and through the upper winding of relay 10 to battery. 35 At armature 1| relay 10 disconnects the busy test conductor of trunk #l at its resting contact and at its Working contact connects up the busy test conductor of trunk`#2 for energizing relay 60, at armatures 12 and 13 disconnects the talkingl con- 40 ductors of trunk #l and connects the talking conductors of trunk #2, at armature 14 completes a locking circuit through its lower winding from springs 55 independent of armature 64, and at armature 15 connects ground to conductor 20 for 45 transfer purposes. Relay 60 now energizes over the following circuit: from ground at the resting contact of armature 69 and said armature, Working contact of armature 1| and said armature, resting contact of armature 6| and said armature, 50 working contacts of spring 5| and said spring, conductor 2, through the induction coil IC, upper cradle springs CS, transmitter T, impulse springs of the calling device CD, conductor push button springs 46, spring 56 and vits Working spring 58, 55 armature 62 and its resting contact, and through the winding of relay 60 to battery. At armature 6| and its resting contact relay 60 opens its own original energizing circuit by disconnecting from the trunk busy test conductor and at its working 60 contact connects the trunk conductor 90 to the local subscribers talking conductor 2 by way of armature 12 and spring 5|. At armature 62 and its resting contact relay 60 opens another point in its own original'energizing circuit and at its 65 working contact connects the trunk conductor 9| to the local subscribers talking conductor by way of armature 13, and springs 58, 56 and 46. At armature 63 relay 60 closes a locking circuit for itself from springs 53 before its original. energiz- 70 ing circuit is opened, at armature 64 opens the original energizing circuit of relay 10 as Well as completing a circuit through the upper Winding of relay 10 from conductor 20 which is grounded at armature 15, and at armature 65 grounds con- 75 andere conductors 90 and 9| and automatically causes the disconnection of. ringing current from the central oihce in the well known manner. Since relay 66 is connected in series with trunk conductor 90 said relay now energlzes from battery at the central office and at armature 68 completes a circuit for energizing busyrelay 61. At armature 69 and its resting contact relay 61 disconnects ground from the trunk busy test conductor 86 to prevent any other local subscriber from seizing this trunk and at its working contact connects the busy tone conductor |28 to conductor 86 to give anothersubscriber, attempting to take this trunk into use, a busy tone.

In case another subscriber should attempt to take this trunk line into use by the operation of key 'TK-2 to answer this trunk call or to originate a trunk call, such subscriber will hear the busy tone. For example, assuming trunk line 2 is busy, then relay 61 is energized to disconnect ground from conductor 86 and connects busy tone in place thereof. Therefore, when the key TK-2 is operated, the relay such as relay 1D is operated but no circuit is completed for the trunk connecting relay such as 60 .because ground is removed from conductor 86 with the result that the calling local subscriber in this case is not connected to trunk 2 and hears the busy tone to inform him that the trunk is busy.

lReturning now to the connection of subscriber #5 to trunk #2, the subscribers receive talking battery from the central office and talk over the heavy talking conductors. After conversation and in response to the replacement of the handset on the cradle the key 'TK-2 and spring assemblies are automatically restored to normal position at which time springs 5|, 52, 55, 56, 58 and 59 are in the position shown in the drawings, while springs 53 and 54 are now open since the handset has been replaced. Cradle springs CS and springs 5| and 56 open the talking circuit to the trunk and relay 66 and latter relay 61 deenergize. At armature 69 relay 61 disconnects the busy tone from conductor 86 and connects ground in place thereof. to enable any local subscriber to seize this trunk in originating or answering a ytrunk call. Springs 53 open the locking circuit of relay 60 which now deenergizes and disconnects the trunk conductors from the local subscribers spring assembly as well as opening the circuit through the upper winding of relay 10. Relay 10 likewise deenergizcs because its locking circuit through its lower winding is opened at springs 55 while the circuit through its upper winding is opened at armature 64. The local subscribers individual equipment including the spring assemblies and the trunk relays are now in normal position.

Since trunk #l is identical to trunk #2 the local subscribers are signalled in a similar manner and any local subscriber may answer an incoming call over trunk #I by operating key TK-I and removing the handset from the cradle. The operation of key TK-I operates all the spring assemblies as described for TK-2 with the exception of spring 55 and therefore no circuit is completed for relay 10. In this case relay 60 is energized over the following circuit: from ground by way of resting contact of armature 19 and said armature, trunk busy test conductor 82, resting contact of armature 1| and said armature, resting contact of armature 6| and said armature, springs 5| and its Working contact, over the subscribers loop to springs 56 and 58, armature 62 and its resting contact, and through the winding of relay 60 to battery. At armature 6| relay 60 disconnects from .-the trunk busying conductor 8| and connects up to the trunk conductor 92, at armature 62 opens the original energizing circuit. of. relay 60 and connects up to the trunk conductor 93, at

armature 63 completes a locking circuit for itself from grounded springs 53 as well asv groundingconductor 22, at armature 611A opens the circuit to relay 10 to prevent its energization, and at armature 65 grounds conductor 2| for transfer purposes. In a manner similar to that previously described the local subscribers line loop is connected over the heavy talking conductors to the trunk conductors 92 and 93 and relays 16 and 11 energize; relay 11 removing ground from conductor 82 to prevent any other local subscriber seizing this trunk and placing the busy tone on a conductor 82 to'give the busy tone to any local subscriber attempting-to thereafter seize the trunk. It being understood that the removal of ground from conductor 82 prevents the energization of the local subscriber'sindividual trunking rconnecting relay, such as relay 60. The release of a connection over trunk #I after conversation is similar to that described for trunk #2.

Outgoing trunk calls busy tone conductor |28, armature 19, conductor p 82, resting contacts of armatures 1| and 6| and said armatures, working contact and spring 5| over the subscribers loop to springs 56 and 58, armature 62 and resting contact and to battery through relay 60. Relay 60 does not energize over this circuit and therefore the subscriber is not connected to trunk #L After hearing the busy tone the subscriber will release the key TK-l and operate key TK-Z to close the same spring assemblies as TK-| and also to close springs 55 to energize relay 10 over the circuit previously traced. Relay 10 disconnects trunk #I and prepares trunk #2 for connection. In case trunk #2 is busy the subscriber will hear the busy tone over a circuit includingarmature 69 and its working' contact, conductor 85, working contact and armature 1|, and thence over the subscribers loop as prev-ouslydescribed. The subscriber will now replace his handset and release the key TK-2 and relay 19 and wait for an interval beiore calling.

In case the trunk #l is idle when the subscriber operated key TK- to originate an outgoing call a circuit may then be traced for energizing relay 69 as follows: from ground at resting contact of armature conductor 82, resting contacts of armature Il and (il, spring 5|, over the calling subscribers loop, springs 56 and 58, armature 62 and resting contact, and through relay 60 to battery. Relay 60 energizes and locks connecting the local subscriber to trunk #l and relays 16 and 11 energize as previously described. In case trunk extends to a manual exchange the operator will answer and complete the call and in case the trunk extends to an automatic e'xchange'the local subscriber waits for dial tone and then operates the calling device CD in acsubscriber for example subscriber #4.

. relay 60. The operation of relays 6U and 'I0 connects the calling subscriber to trunk #2 after which the trunk calls are completed as previously described.

Holding circuit Any local subscriber can hold a trunk call while either making or answering a local call by restoring the operated trunk key to normal. The restoration of the trunk key without replacing the handset disconnects the local calling subscribers loop from the trunk line and connects it to its local line and also closes a holding bridge for the trunk line. When the trunk key is restored springs 5| and 56 are restored to normal, while spring 52 and spring 53 (in case TK-I was operated) are held locked in operated position by catch 51. Spring 53 maintains relay 60 energized over its locking circuit and maintains conductor 22 grounded. In case TK-'Z had been operated then `spring 55 maintains relay lil energized and conductor 23 grounded. The holding circuit for either trunk may be traced from armature 12, working contact and armature 6I, through the impedance coil, locked springs 52, springs 54, springs 59 and 58, armature 62 and its working contact to armature 13. As will be seen springs 56, 58 and 59 are a make before break combination to insure the closing of the holding circuit before the trunk is disconnected from the subscribers loop. The trunk connection is held over this holding circuit while the local subscriber either originates or answersI a local call and by the reoperation of the proper trunk key vthe local subscriber can return to the trunk and release the local connection. Since the busy trunk relays, such as 61 and 11, are maintained energized while the trunk is being held the trunk is made busy to all other local subscribers lines.

Transfer circuits A local subscriber can transfer a trunk connection to any other local subscriber by releasing the trunk key thereby holding the trunk connection over the holding circuit and then connecting with the desired local subscriber over the local finder connector links. The transfer arrangement is designed so that only the called local subscriber, after being called by the local subscriber holding the trunk connection, can connect with the held trunk line, while all Athe other subscribers lines are unable to connect to the held trunk line. If desired both local subscribers may remain connected to the held trunk line and may also transfer the call to a third. local subscriber.

It will now be assumed that local subscriber #5 is connected in a trunk call to the central ofce over trunk #I and that the central oice subscriber desires to converse with another local In order to transfer the call subscriber #5 restores the operated trunk key TK-I, thereby establishing the holding circuit for trunk #I as previously described. Since the local subscriber did not replace the handset, the subscribers loop is connected to the local line conductors 3| and 32 to cause the energization of common line relay 8 and cut-olf relay 4 in its tlrst step as previously described. In the same manner as described for a local connection the nder F is operated to ilnd the calling local line and the subscriber operates the connector C to connect with and ring the called subscriber, in this case the subscriber #4. When the called subscriber answers the calling subscriber advises the subscriber #4 that such subscriber is wanted on a trunk connection over trunk #I. Relay |60 energizes when the called subscriber answers and at armature |65 necting relay connects the talking conductors 8| and 85 of trunk #I to the spring assemblies in the sub-base of subscriber #4 in a manner apparent from the similar spring assemblies and sub-base shown in detail inV Fig. 1. 'Ihe trunk connecting relay, similar to relay 60, also completes its own locking circuit from ground at springs similar to springs 53 by way of the armature similar to armature 63. From the foregoing it will be seen that subscriber #4 is prepared for connection with trunk #I in response to the operation of the subscribers individual trunk connecting relay While trunk #I is still maintained busy to all the remaining local subscribers since no means is provided for energizing their individual trunk connecting relays. In order to pick up the trunk connection, subscriber #4 will operate the trunk key for trunk #I without replacing the handset to the cradle. Subscriber #4 is now connected to trunk #I over the trunk conductors 8| and 85. shown in Fig. 1, which are connected to conductors 8| and 85 shown in Fig. 2 and from thence through the armatures on the trunk connecting relays, similar to relays 60 and 10, to the spring assemblies and subscribers loop individual to the subscriber #4, similar to the spring assemblies and subscribers loop shown in Fig. 1 individual to subscriber #5. Subscriber #5 will now reoperate key TK-I and reconnect with trunk #L When the subscriber operates key TK-I the finder connector linkis restored to use in the same inanner as previously described and may be used on subsequent calls. If desired subscriber #5 may remain connected to trunk #I along with subscriber #4 or may release from the connection by replacing the handset on the cradle. This operation releases the spring assemblies 'and opens the locking circuit of relay 6I) which deenergizes. Subscriber #5 cannot come back on the trunk connection unless subscriber #4 calls subscriber #5 locally While maintaining the trunk connection. The reason for this is apparent from the foregoing description because no circuit is provided for energizing relay 60 when the trunk #I is busy. Subscriber #4 may transfer the trunk connection to another local subscriber, if desired, in the same manner as just described. y

It will now be assumed that subscriber #5 is connected in a trunk connection over trunk #2 and that such subscriber desires to transfer the connection to subscriber #4. In this case in order to transfer the call, subscriber #5 restores the key 'TK-2 thereby establishing the holding circuit for trunk #2 as previously described. Relay 6|!A remains locked in energized position over spring 53, and relay '|0 remains locked in energized position from ground at armature 15, armature 64 and its working contact, and through the upper winding of relay 'I0 to battery. The local connection to subscriber #'is established over the finder connector link in the same manner as previously described and when subscriber #4 answers relay |60 energizes and completes energizing circuits for both trunk connecting relays individual to subscriber #4 since both conductors 20 and 2| are grounded. The circuit for energizing the trunk connecting relay corresponding to relay I may be traced as follows: from ground at armature "I5, conductor 20, fifth finder bank and wiper |03, armatures |64 and |98, wiper |09 and fourth connector bank, conductor 23', through the normally closed springs controlled by the armature, similar to armature 64, and through the upper Winding of the trunk connecting relay, similar to relay 10, to battery. Thea circuit for energizing the trunk connecting relay, similar to relay 60, is the same as that previously described over conductors 2| and 22'. As will be noted, the trunk connecting relays, such as relay 69, are slow to operate and therefore the relays, such as 10, energize and prepare locking circuits for themselves before the relays, such as relay 60; fully operate. When the trunk connecting relay similar to relay 60 fully operates and locks as previously described, such relay at the armature corresponding to armature 64 completes a locking circuit for the relay corresponding to relay 10. This locking circuit is similar to the locking circuit for relay 'I0 shown in Fig. 1 which extends by way of armature 15, armature 64 and through the upper winding of relay 10. The operation of the trunk connecting relays individual to subscriber #4 connects the talking conductors 83 and 84 of trunk #2 to the spring assemblies in the sub-base of subscriber #4 preparatory to connecting trunk #2 to subscriber #4. In order to pick up the trunk connection, subscriber #4 will operate the trunk key for trunk #2 without replacing the handset. Subscriber #4 is now connected to trunk #2 over trunk conductors 83 and 84, shown in Figs. 1 and 2, through the operated armatures of the trunk connecting relaysr to the spring assemblies and local line loop individual to subscriber #4. If desired subscriber #5 may reoperate key TK-2 and remain in the trunk connection with subscriber #4 or may release from the connection by replacing the handset on the cradle. 'I'he replacement of the handset on the cradle restores the spring assemblies `to normal and causes the deenergization of re- Allotter operation A second local call by any local subscriber energizes the common line relay 8 over conductor 3 in a manner similar to that previously described. However, in this case since relay I0 is locked locally, a start circuit is now closed for start relay |20' ofthe second finder connector link. 5

This circuit may be traced as follows: from grounded armature 9, armature I2 and its working contact, through the lower winding of relay II, conductor I6', winding of start relay |29', armature |45', normal bank` contact and wiper |08 to battery through the Winding of the connector motor magnet of the second finder connector link. A branch of this circuit may be traced from the working contact of armature I2, armature I5, throughthe upper winding of relay II, armature I4, to conductor I6. 'Ihe two circuits traced `through both lower and upper windings of relay II assist each other to quickly energize relay II. Another circuit is also closed by way of armatures 9 and I2 by way of armature 20 I5 and conductor I5 for the start relay |20 of the first nder connector link, but since start `relay is slow to operate relay will operate its armature |5 to open the circuit to relay |20 before the same can fully operate. In response to the operation of start relay |20 the nder of the second finder-connector link is operated to find -the calling line after which the connector of the link is directively operated to connect with the called line in a manner similar to that previously described. When the nder nds the calling line the release relay in the second link, corresponding to relay |30, energizes and at armature |32' grounds conductor I1 by way of armature |22 to short circuit relay I0 thereby causing the latter`35 relay to deenergize. This short circuit extends from grounded conductor I1' through the Winding of relay I0 to ground at armature I3. The

calling subscribers cut-oir relay. such as 4, is now yfully operated so that the common line relay 8 deenergizes to open the start circuit to the second link and when relay I0 is fully deenergized the start circuit for the first link is prepared at armature I2 and its resting contact. From the foregoing it will be seen that a two-relay allotter has been provided for alternately taking the two links into use on successive calls.

Some provision should be made for taking into use an idle one of the links when the other is busy although the said otherl link is prepared for seizure by the alternate two relay allotter. For example, it will be assumed that the first finder connector link shown in Fig. 2 is idle having been seized and released on a call of short duration subsequent to the call now maintaining the second finder connector link busy. In this case in the two relay allotter relay I0 is locked in its energized position ready to seize the second link. Now if a call should be originated at this time relay 8 will energize as before to close the start circuit. In this case since the second link is busy the start circuit therein is open at armature |45 or at theA connector banks, with the result that neither the start relay |20' of the second link or relay I can energize. In this case the start circuit now extends from groundedv armature 9, arrnature I2 and its'wcrking contact, armature I5 since relay II is not energized, conductor I6, relay |20 of the first link and over the previously traced circuit to battery through the connector motor magnet |35. This same condition also exists in case of open or dirty contacts in the start circuit. From the foregoing it will therefore be seen that the allotter seizes the first link instead of the second link when the first link is idle and the second busy at a time when the allotterfhas been set to normally allot the second link. The reverse of these conditions, that is, the allotter seizes the second link instead of the first link when the second link is idle and the iirst busy at a time when the allotter has been set to normally allot the iirst link, is also provided for and in such cases the relay I0 would be in normal position.

In case both the iirst and second links are busy the calling subscriber will not hear dial tone and will either wait until one of the links becomes idle or will replace the handset on the cradle. A

Having described the invention, what is considered to be new and is desired to have protected by Letters Patent will be set forth in the following claims:

What is claimed is: A

1. In a telephone system, a local exchange, a distant exchange, a trunk connecting said exchanges, a plurality of local subscribers lines in said local exchange, a trunk connecting relay individual to cach subscribers line for connecting such subscribers line to said trunk line, subscriber controlled means for operating its individual trunk connecting relay to connect such `subscribers line to said trunk line in case saidy trunk line is idle, and a relay in said trunk operated in case the trunk is busy for preventing the operation of any trunk connecting relay in response to the operation of said subscriber controlled means.

2 In a telephone system, a local exchange, a distant exchange, a trunk connecting said exchanges, a plurality of local subscribers lines in said local exchange, a trunk connecting relay individual to each local line for connecting such subscribers line to said trunk line, a circuit common to said trunk connecting relays over which said relays are energized, subscriber controlled means for completing said circuit to energize only its individual trunk connecting relay to connect such subscribers line to said trunk line in case said trunk line is idle, and a relay individual to said trunk for opening said circuit when the trunk is busy to prevent the energization of any trunk connecting relay in response to the operation of said subscriber controlled means.

3. In a telephone system, a local exchange, a distant exchange, a trunk connecting said exchanges, a plurality of local subscribers lines in said local exchange, a trunk connecting relay individual to each local line for connecting such subscribers line to said trunk line, a circuit common to said trunk connecting relays over which said relays are energized, subscriber controlled means for completing said circuit to energize only its individual trunk connecting relay to connect such subscribers line to said trunk line in case said trunk line is idle, a relay individual to said trunk for opening said circuit when the trunk is busy to prevent the energization of any trunk connecting relay in response to the operation of said subscriber controlled means, and a busy tone source controlled by said individual trunk relay connected to a subscribers line in response to the operation of said subscriber controlled means when said trunk line is busy.

4. In a telephone system, a local exchange, a distant exchange, a trunk connecting said exchanges, a plurality of local subscribers lines in said local exchange, a trunk connecting relay individual to each local line for connecting such subscribers local line to said trunk line, a circuit for each of said individual trunk connecting reat such trunk line to prevent the energization of lays, individual subscriber controlled means for completing the circuit to energize its individual trunk connecting relay to connect such subscribers line to said trunk line in case said trunk line is idle, and a relay individual to said trunk 5 line for opening said circuits when the trunk line is busy to prevent the energization of said trunk connecting relays in response to the operation of said subscriber controlled means.

5. In a telephone system, a local exchange, a 10 distant exchange, a trunk connecting said exchanges, a plurality of local subscribers lines in said local exchange, a trunk connecting relay individual to each local subscribers line for conl necting such subscribers line to said trunk line, 15 a circuit for each of said individual trunk connecling relays, each said circuit including a common portion individual to said trunk line, an, operating potential normally connected to said. common portion for producing current for ener- 20 gizing said trunk connecting relays, a busy tone source, a relay individual to said trunk line for4 disconnecting said operating potential from said common portion to prevent the energization of saidtrunk connecting relays and for connecting."'25 said busy ,to'ne' source to said common portion when said trunk line is busy, and individual sub- A scriber controlled means for completing its indi-` vidual circuit over said common portion and said operating potential to energize the subscribers. 30 individual trunk connecting relay to connect such subscribers line to said trunk line incase said trunk line is idle and for connecting said busy tone source to said subscribers lineover said common portion in case said trunk line is busy. 35 6. In a telephone system, a local exchange, a distant exchange, a plurality of trunk lines connecting said exchanges, a plurality of local subscribers lines in said local exchange, a trunk connecting relay individual to each local line for 40 connecting such subscribers line to said trunk lines, a circuit for each of said individual trunk connecting relays, each circuit including a common portion individual to each of said trunk lines, an operating potential normally connected to said common portion at each trunk line for providing current for energizing said trunk connecting relays, a busy tone source, a relay individual to each trunk line for disconnecting said operating potential from said common portion said trunk connecting relays and for connecting said busy tone source to such common portion when such trunk line is busy, and individual subscriber controlled means for each trunk line for selectively connecting such subscribers line to the trunk line corresponding to operated individual subscriber controlled means by completing the individual circuit to energize the individual trunk connecting relay over said operating potential and said common portion individual to such trunk line in case such trunk line is idle and for connecting said busy tone source to said subscribers line over said common portion individual to such trunk line in case such trunk line is busy. 65 '7. In a telephone system, a local exchange, a distant exchange, a plurality of trunk lines connecting said exchanges, a plurality of local subscribers lines in said local exchange, a plurality of trunk connecting relays individual to each 70 local subscribers line for connecting such subscribers line to said trunk lines, individual subscriber controlled means for each trunk line for selectively operating said trunk connecting relays to connect such subscribers line to the trunk 75 line corresponding to the operated subscriber controlled means in case such trunk line is idle, and a relay individual to each trunk line oper-` ated in case the trunk line is busy for preventing the operation of one of said individual trunk connecting relays in response to the selective operation of any one of said individual subscriber controlled means in case said trunk line is busy.

8. In a telephone system, av local exchange, a distant exchange, a trunk connecting said exchanges, a local subscribers line in said local exchange having a local substation line loop, a trunk connecting relay individual to said subscribers line, subscriber controlled trunk connecting means, an individual circuit for energizing said relay including contacts on said relay and said substation loop completed responsive to the operation of said trunk connecting means, and means including said contacts and said trunk connecting means for connecting said trunk line to said substation loop in response to the operation of said relay.

9. In a telephone system, a local exchange, a distant exchange, a trunkA connecting said exchanges, a plurality of local subscribers lines in said local exchange, each having a local substation line loop, a trunk connecting relay individual to each local subscribers line, Working contacts on each of said relays normally disconnecting said trunk line from said local subscribers lines, an individual circuit for energizing each saidA relay, each circuit including 'resting contacts on its individual relay and the subscribers local line loop, and subscriber controlled means for connecting said subscribers local line loop to said resting contacts to energize its individual relay to connect said working contacts and trunk line to said subscribers local line loop.

l0. In a telephone system, a local exchange, a distant exchange, a plurality of trunk lines connecting said exchanges, a local subscribers line in said local exchange having a substation line loop, a trunk connecting relay individual to said subscribers line, subscriber controlled trunk connecting means for each trunk line, an individual circuit for energizing said relay including contacts on s-aid relay and said substation loop completed responsive to the operation of any one of said subscriber controlled trunk connecting means, and means including said contacts and the operated trunk connecting means for connecting the sub:tation loop to the trunk line corresponding to the operated trunk connecting means in response to the operation of said relay.

1l. In a telephone system, subscribers lines, a pair of finders having access to said lines, a relay allotter for normally preselecting said iinders alternatively regardless of their busy or idle conditions on successive calls, and means responsive to the initiation of a call on one of said ylines in case the preselected nder is busy for operating said allotter to seize the other iinder if idle.

12. In a telephone system, subscribers lines, a pair of finders having access to said lines, a relay allotter vfor normally preselecting said nders alternatively on successive calls, means responsive to the initiation of a call on one of said lines for operating the preselected nder if idle to connect with the calling line, and means responsive "to the initiation of a call on one of said lines in case the preselected nder is busy for operating said relay allotter to seize the other inder if idle and operate such nder to connect with the calling line.

13. In a telephone system, subscribers lines, a pair of finders having access to said lines, a relay allotter for preselecting said iinders, means responsive to the initiation of a call on one of said lines for operating the preselected finder. it idle 5 to connect with the calling line, means responsive to said connection for operating said allotter to preselect vthe alternate finder regardless of its busy or idle condition, means responsive to the initiation of another call by another one of said 10 lines for operating the preselected alternate ilnder if idle to connect with this calling line, means responsive to this last connection for operating said allotter to preselect the ilrst finder regardless of its busy or idle condition, means for reu leasing the alternate finder after conversation, and means responsive to the initiation of a third call by any one of said lines for operating the relay alotter to seize the -alternate finder if idle and to operate it to connect with the calling line lo in case the preselected rst finder is still busy in said first connection.

14. In a telephone system wherein a plurality of subscribers lines are each provided with a trunk key for originating and answering trunk g5 calls over a trunk line connected to a distant exchange, a trunk connecting relay individual to each subscribers line; means enabling the operation of such relay in response to the operation of its individual trunk key only if said trunk line 30 is idle, for connecting said trunk line to such subscribers line; means for holding a trunk call while such subscriber completes a local connection to another local subscribers line, and means responsive to the completion of said local connection for operating the trunk connecting relay individual to said other subscribers line while said trunk is being held.

15. In a telephone system wherein a plurality of subscribers lines are each provided with a 40 trunk key for originating or answering trunk calls over a trunk line connected to a distant exchange, a trunk connecting relay individual to each subscribers line operated in response to the operation of its individual trunk key in case said trunk line is idle and inoperative in response to the operation of said trunk key in case said trunk line is busy, each relay when operated connecting said trunk line to the subscribers corresponding trunk key, means for holding a trunk call while a subscriber completes a local connection to another subscribers line, and means responsive to the completion of said local connection for operating the trunk connecting relay individual to said other subscribers line. l

16. In a telephone system wherein a plurality vof subscribers lines are each provided with a trunk key for originating or answering trunk calls over a trunk line connected to a distant 00 exchange, a trunk connecting relay individual to each subscribers line operated in response to the operation of its individual trunk key in case said trunk line is idle and inoperative in response to the operation of said trunk key in case said a5 trunk line is busy, each relay when operated connecting said trunk line to the subscribers corresponding trunk key, means for holding a trunk call while ya subscriber completes a local Y connection to another subscribers line, means responsive to the completion of said local connection for operating the trunk connecting relay individual to said -other subscribers line, and means thereafter responsive to the operation oi' the trunk key individual to said other sub- 76 scribers line for connecting said other subscribers line to said trunk line.

17. In a telephone system wherein a plurality of subscribers lines are each provided with a plurality of trunk keys for originating and answering trunk calls over a plurality of trunk hues connected to a distant exchange, a trunk connecting relay individual to each subscriber's line operated in response to the operation of any one of individual trunk keys ii the trunk line corresponding to the operated trunk key is idle for connecting such trunk line to such subscribers line, means for holding a trunk call while a subscriber completes a local connection to another local subscriber's line, and means responsive to the completion of said local connection for operating the tnmk connecting relay individual to said other subscribers line. Y

18. In a telephone system wherein a plurality of subscribers lines are each provided with a plurality of trunk keys for originating and answering trunk calls over a plurality of trunk lines connected to a distant exchange, a trunk connecting relay individual to each subscriber's line operated in response to the operation of any one of said individual trunk keys if the trunk line corresponding to the operated trunk key is idle for connecting such trunk line to such subscribers line, means for holding a trunk call while a subscriber. completes a local connection to another local subscribers line, means responsive to the completion of said local connection for operating the trunk connecting relay individual to said other subscribers line, and means thereafter responsive to the operation of said other subscribers trunk key corresponding to said held trunk for connecting said other subscribers line to said trunk line.

19. In a telephone system wherein a subscribers line is provided-with a plurality of Y,

trunk keys for originating and answering trunk calls over a plurality of trunk lines connected to a distant exchange, a trunk connecting relay individual to said subscribers line, means for operating said relay in response to the operation of any one of'said individual trunk keys if the trunk line corresponding to the operated trunk g keys is idle for Yconnecting such trunk linel to y said subscribers line, and means for rendering said relay inoperative to connect said trunk line with said subscribers line in response to the Vof subscribers lines are each provided with a plurality of trunk keys for originating and answering trunk calls over a plurality of trunk lines connected to a distant exchange, a rst and a second trunk connecting relay individual to each subscriber's line, means for operating the first of said trunk connectingrelays only in to the operation of a particular one of said Vindividual subscribers trunk keys to select the corl responding particular trunk line and prepare it for connection with such subscriber's line, means for operating the second of said trunk connecting relays in response to the operation of said particular key or any other individual trunk conl0 necting key only in case the trunk line correspending to the operated trunk key is idle for connecting such subscriber's line to the trunk line corresponding to the trunk key operated, means for holding -a trunk call while the subscriber l5 completes a local connection to another local subscribers line, and means responsive to the completion oi said local connection for operating the corresponding trunk connecting relays individual to said other subscriber's line. M 21. In a telephone system, a local exchange, a distant exchange, a trunk connecting said exchanges, a plurality of local subscribers lines in said local exchange, means for completing local connections between local subscribers lines in- Vplurality of individual local subscnbers' um in said local exchange, subscribers substation circuits normally connected to their individual lines. 40 means for completing local connections between local subscribers substation circuits over theirY individual lines, a distant exchange, a trunk connecting said exchanges, a trunk connecting relay individual to each subscriber's on 45 circuit for connecting such subscriber's substation circuit to said trunk line. subscriber controlled means for disconnecting the subscriber's substation circuit from its individual line and for operating its individual trunk connecting relay in connect such subscriber's substation circuit to said trunk in case the trunk is idle, and a relay insaidtrunkoperatedincasethetrunkisbusy Afor preventing the operation of any trunk connecting relay inresponse to the operation of said 55 subscriber controlled means.

JOHN H. Voss. HARRY N. Nnws'rnm. 

